1. Field of the Invention
The present invention relates to a storage system and a method for copying data among a plurality of sites.
2. Description of the Related Art
A storage system, for example, comprises at least one storage controller, called a disk array subsystem or the like, and provides data storage services to a host computer (hereinafter, “host”). A storage controller, for example, can arrange a large number of disk drives in an array, and can construct a storage area based on RAID (Redundant Array of Independent Disks).
Further, as with so-called disaster recovery systems, it is also possible to install a backup site in a distant location from a main site in preparation for a regional-scale disaster. A backup storage controller is installed at the backup site, and the same data groups as the main site are stored in this storage controller.
In a first prior art, it is possible to prepare for a regional-scale disaster by remote copying data from the storage controller of the main site to another storage controller at a backup site (Japanese Patent Laid-open No. 2005-215885). Consequently, even if the main site is shut down due to failure, data processing services can be continued using the backup site. However, if a failure should occur at the only backup site before the main site recovers, data processing services can no longer be provided to the host.
Accordingly, a second prior art is proposed by which a plurality of backup sites are provided so that system redundancy can be ensured even when the main site is down (Japanese Patent Laid-open No. 2005-84953). In this second prior art, a plurality of secondary storage controllers are respectively connected to a primary storage controller as disclosed in paragraph numbers 0008 through 0010 thereof. When the storage content of the primary storage controller is updated, this updated content is immediately sent to one of the secondary storage controllers, and reflected in the storage content of the one secondary storage controller. Further, the storage content of the primary storage controller is stored as journal data, and the other secondary storage controller arbitrarily reads out this journal data and reflects same in its own storage content. Then, the one secondary storage controller creates journal data based on a data update command from the main storage controller, and stores this journal data. When the main storage controller goes down, the other secondary storage controller reads out journal data from the one secondary storage controller, and updates its own storage content.
In the prior art, data copies are maintained by either two sites or three sites, thereby making it possible to heighten resistance to disasters and the like. However, even when three sites are provided, the reliability of data protection decreases if any one or two of the sites fail. Accordingly, it will most likely be necessary to maintain copies of data at more numerous sites in order to heighten data protection reliability.
In the case of a constitution in which a copy path for remote copying is established between a plurality of sites, and data is copied to the respective sites, if a failure occurs in a portion of the sites or in the communication path between sites, it is necessary to reconfigure the copy path using normal sites and communication paths. However, the more numerous the sites involved in remote copying, the more difficult it is to reconfigure a copy path subsequent to a failure occurring. This is because of the need to reconfigure the copy path taking into account the order of data written from the host, and the direction of remote copying.